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Full text of "On wire ropes [microform]"

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Canadian Institute for Historical IMicroraproductions / Institut Canadian da microraproductions historiquas 




1996 



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1 2 3 




1 2 3 

456 



MICBOCOPY RESOLUTION TIST CHART 

lANSI ond ISO TEST CHART No. 2) 




I.I 



1^25 ji 1.4 



: iiiiiM 
■ Ilia 



1.8 



^liilU^ 



^ -^jPPUEDJVMGE 






>. 



r> 



On Wire Ropes. 

By W. I). 1,. llAKi.m, M.l'., I.elhliriiiKe, Alta. 
That wire rope as a mechanical means of cheaply conveying coal 
IS being superceded by electricity and comijrcssed air is not admitted 
by many mining engineers. 

After many years of careful study of lb-.' three systems ano closely 
watching the actual application of the •. all, we are fully convinced 
that wire rope haulage will live on after some of the new fangled 
systems have settled down to their proper sphere. That compressed 
air and electricity have many advantages in some respects, it is not 
our purpose to controvert, but that wire rope haulage actuated by 
steam, electricity or compressed air has a wider field than either the 
compressed air or electrical locomotive is our contention. If 
this be admitted as correct and, whether or no, it certainly is the 
duty of all mining engineers and colliery managers to have as 
complete a knowledge about wire ropes as is possible in one having so 
many diversified duties to p'-rform, so that he will not be entirely at 
the mercy of the rope manufacturer who has his little " trick of trades " 
in common with most other manufacturers. 

It is the writer's intention in this short |iaper to give some practical 
and theoretical notes on wire ropes, not claiming any originality, in 
the hope that they may be beneficial to the younger members of the 
profession. 

Wire ropes for mine use are generally composed of : 

(i). Six wire strands composed of s»ven wires each, twisted on a 
hemp centre. 1 ne centre wire of the st' Mid sometimes being soft. 

(2). Six wire strands composed of twelve wires each, twisted on a 
hemp centre. 

(3). Six wire strands, composed of nineteen wires each, twisted on 
a hemp centre. 

This construction is sometimes varied so that there are 13 larger 
wires and 6 smaller wires in each strand, but the general construction 
of the rope is the same. 



\.. 



' The Canaiiian Mining Imtilute. 

The ratios of the diameter of the individual wires to the diameter 
of the rope in these three cases, not including the rope with two sized 
wires as in No. 3, are as follows : (,) ., (,, ;^., (3, ,,.. prom this, 
the gauge of wire required to conFtitute a rope can readily be got to a 
close apiiroximaiion. 

No. I is only used where large wheel drums and easy curves 
can be employed. Such a condition does not very often present itself 
in coal mines. The No. .. rope is a more pliable one and can be used 
on smaller drums, wheels, and curves, Imt when we remember that the 
size of tlie individual .vires govern the si/e of wheel it will be seen that 
with this rope, with a heavy load, such as is usual in mine haulage, 
the wheels would be relatively large. \ wire shouM not be bent over 
a wheel less than .,000 times i;s diameter for good lesulis in length of 
life and tons hauled. 

Excepting in ropes of large diameter No. 3 is not used for mine 
haulage but is largely em])loyed for hoisting ropes. 

To meet the conditions of severe bending usual in the underground 
working of collieries the British manufacturers construct a compound 
rope which we will designate as (4) : 

(4). Six wire strands, each composed of 9 large wires twisted 
around 7 smaller wires (the centre or seventh wire being soft), twisted 
round a hemp centre. The gauges of wire used and number of wires 
used in the construction of a compound rope are varied to suit the 
circumstances. These ropes are very servicable and meet the mine 
manager's wants with a wonderful degree of satisfaction. 

I am not aware that any American rope makers are constructing 
ropes of this style. 

In computing me strength of any twisted wire rope it is well to 
remember that the strength of each individual wire is reduced from 
4 per cent, to ,0 per cent, by twisting. The makers claim the strength 
IS reduced 4 per cent, while disinterested experimenters claim the 
strength is reduced .0 per cent. Perh.aps a fair allowable reduction 
of strength for twisting in manufacturing, would be the average of the 
two, viz : 7 per cent. 

Iron wire rope.5 are not suitable jr mining purposes and are not 
considered in this paper. 



911960 



■♦■ Tsss^^ srsn"*"*"- 



Oil IViir Kofes. 



t> 



There is a very wide ranfje in the grades of steel ropes and as tlie 
breaking strengtii per s(|iiare inch of section of ihe material of ivhicli 
they are constructed is fundamenial, we herewith give a short tahle 
which will make the point clear. 



r<l oi Cnii-il.lc Slul. 



Tons. 



■r.iii. tmiis r,,!!,. ]■,, 



The ipiality here is in tons of 2,240 lbs. per square inch of 
section. 

The composition that enters into these grades is partly a secret of 
the manufacturer, however, a vast amount of information has been 
published but the articles are too numerous and conllicling to he 
brought within the limits of this paper. 

For the purpose of making the above tables clear let us take an 
example: -Suppo.se we are going to use a crucible steel rope is-ifi 
inch diameter, or 3 inches circumference, composed of six strands, each 
strand having 9 wires .080 inch diameter, twisted over 7 wires .054 
inch diameter, of 201,600 lbs. breaking strain per square inch, what is 
the breaking strain of the rope .^— 

.082 in. X .7,854 .\ 201,600 lbs.= 1008" X9 wires. 9,.)72 lbs. 
.0542 in, X .7,854 X 201,600 lb5.= 4fii.7'-x6*wire.5. 2,77olbs. 



St 



rengi; 



of one strand 1 ,,,S42 Ihs. 

6 



11,842 lbs. X 6 strands ■> 1,052 lbs. 

Less 7 per cent, allowed for twisting 7,105 lbs. 



Breaking strain of rope 63,947165. 

t The safe working load in underground haulage 

may be from 1.7 to 1-5 say 1-6 10,658 lbs. 

* Six of the seven small wires only enter into this calculation as 
the seventh wire is the core of the strand and is soft having little 
tensile strength. 



Thf Oinadian AfiiiiHg Imlilule. 



t A rope running at a low speed and no lives depending upon it, is 
not subject to the sudden strains ol' a high speed rope and may have a 
very low nicior of safely. In slow endless rope haulage i-j miles per 
hour, we iliink, •; is a safe factor. Hut with fast running tail-ropes 7 is 
not toil ,irge. For hoisting ropes the safe factor should be 10. 

The following we regard is a good sample of a specification for 
wire rope : — 

Qiiiirv iif mir.—i. All steel used in ihe manufacture of the 
cable shall be of 1 he "best scleclcd i)atent in-iiroved crucible steel" 
drawn to a uniform diameter throughout, and ■:a,,..ble of withstanding 
the lists tncntioned in the table given bcljw. 

r.iiij;l/i, in,' anu'/orm 0/ H^'h,- 2. The c.ule shall be 

feet long ..id shall have a circumference of 35 a inches (three and 
five eighths) when finished. It shall consist of six outside strands laid 
u]) in the formation known a^ the '■ Lang lay," with Ihe lay in the rojie 
in the same direction as the lay in the strat.Js. 

Stiaiidi. — T,. Each strand shall he composed of seven wires .115 
mch in diameter, laid round a core consisting of five wires .061 inch 
in diameter round one wire .049 inch diameter. 

Spinning.— ^. Kacli strand shall be spun in feet lengths and 
evenly woimd ilirect from the machine on to a reel. When it is 
necessary to join either tne outside or inside wires they sh.all be pro- 
perly scarfed and brazed. 

Chsing.—^. The si.x strands shall be closed under i.iiform tension 
round a heart consisting of the best white manilla rop», having three 
strands, hard laid, and well soaked in oil. 

l,iy.—6. The lay of the wires in the strands shall le 53,| inches 
(three and three-quarters) .ind the l.iy of -he strands in the cable y'/, 
inches (nine and one half). 



I 



On IVire Kcfrt. 



f 



TABLKS OF TKSTS- 7. 

TKNSII.K IHST. 



T)i;mteter 
of wire. 



iisidch. 
.061 *■ 
.049 " 



UiiKthof let, T*-"!*'!* l«t. i 
piece betwreii , Streai 

gauge itiark*. Mr*M per per wire, 

•quare inch. 



H inchei . 
H " 



90 lotlH 
85 •• 



>,<i94 Iba. 
55« " 
359 ■• 



Here Ihe core wire of the slrand is not soft as in the case we 
made the calculation for. 

Ul'CTtl.K TKST. 



Lingth of tMt, 
piece between 
gauge marks. 



K inches. 
8 " 
8 •■ 



Nui.iber 
of twista. 



25 number. 

45 

5S " 



B^nds to IS<)° 

over o-*e-nuarter 

inch radiua. 



^ nunibei. 
6 



radi Hank to be siiUfclcd to t,-sl.—%. Uefore proceeding with the 
manuacture of tne cable, the contractor shall submit every ha nl. of 
wire to the engineer, who wii: make tensile and ductile tests from each 
end of the hank before it is worked into the cable. 

ya,i,itim from sptcified trsls.—g. Kvery hank wiiich shall be 
found to vary more than 2'/, |,er cent, in either direction from the 
tensile tests specified above, or more than 8 per cent, below the 
specified number of twists in 8 inches will be rejected. 

Test of Call/,:— to. The contrac'or shall make the cable suffi- 
ciently long to allow for cutting off a suitable portion which shall be 
lested for tei sile strength in the jiresence of the engineer, or his repre- 
sentative, and must withstand a load of 4.? tons (ton here is 2,240 lbs.) 
without breaking. 

Costof making tests.— II. The cost of all tesis, whether made at 
the contracto '- »n-ks or elsewhere, shall be borne by the contractor. 



iHe Omadian Mining Institute, 



Otrmi^^ii t.it\.—\2 In addition to (he aliovc, rhcmicil tcstH may 
iif made at ihu liHcretion oj the engineer. 



Curliori 

Silicon 

Mimganciit- . 
liiosphoniH . 
Sulphur 



t nitir wire. 


Inner wire. 


Coie wire. 


MS in. <lititii. 


.nfi 


in. diam. 


.(i.l<) In. Hiani 


5" 

.11*) " 




• S" 
Of, ■■ 


• 5" 


.,Vi " 
."4.1 '■ 




.JO " 


.,S" " 
"4.1 ■' 
.04.1 •■ 



"Manganese imparls loiiijiincss and nculraiiscs •■shorlness," it 
furlhcr acts in favor of il.c presence and functions of the carlmn." 
Silicon can only Iw tolerated in very limited riuantities, wliilst jihos- 
phorus and sulphur are the greatest enemies encountered in the 
manufacture of steel. Any excess of silicon produces brittleness, 
wliich is more marked as the percentage of carbon is raised. Small 
■ luantities of sulphur present in steel will produce unsoundness and 
"red shortness" whilst phosphorus is detrimental on account of 
causing " cold shortness " besides being an enemy to any form of 
tempering and conductivity."— iw/M. 

In the ordinary construction of wire rojies the wires forming the 
strands are twisted to the left hand but the strands are tivisted to the 
right hand, or opposite direction. In die " I.ang lay " the wires form- 
ing the strands and the strands comprising the rope are all laid in the 
same direction. Ropes may be laid up "right" or "left" hand and 
this is no small consideration in the life of a ro|)e if one coil chafes on 
another. If, when standing behind the drum facing the pit head 
pulleys, the rope travels on drum from left to right, the rope should be 
laid "right handed," or vice versa. The tendency 10 mount and side 
friction are miiiimised. 

The "lays" adopted in wire rope inaking are principally dependent 
upon the gauge of the wires em]>loyed, the size of the rope to be made, 
and the purposes they are intended for. .Approximately it may be saiti 
that the "lays" in strand, vary about ihree to four times the diameter 
of the rope and the " lays" in the rope vary from seven to ten times 
the diameter of the mpe. 

The average elongation of ordinary constructed ro|)e is about 
.3 percent, and with "Lang lay" ,'/, percent, to j per cent, which 



On lliir A'k/vs 



mint not l« lo.t sight of in hoisting rope> and endless rope. ,\ ,,„,. 
able tiKhtcning arrangement wii] take up ihf elongation in endless ropes 
but in hoisting ropes it is a case of pullinj, t .e rope up in the fasten- 
ings in the drum. 

With hoistinn rop.i ihe life can be greatly i,„ reased by ordering 
sufficient length to enable 6-10 feet to be cut off the end periodically 
and thus change the point of lift or stress. 

It IS of ih. rsi importance th:it ropes be greased i- . uently and 
carefully with ., good, pure, grease which is absolutely u.^ rom acids. 
A greab^' with acids in it is worse ihan no grease. 

I is obvious where ropes have to bend round wheels, drums, or 
cf • 's, that the outer fibres of ,„».', win; as they accommodate them 
selves to the curvature, are in tension, and the inner wiies in com 
pres-sion, whiL the center or neutral axis is unchanged. As a con- 
sequence it may be assumed that ihe more Hexible a rope, ,. ,-. offers 
less resistance in compression and tension in each wire, where it is 
subjected to much ,inding in work, the belter will be the results, pro- 
vided that such f bilily be not obtained by the use of such line wires 
that the wearing capacily of the rope is affected. 

We said in the early |)art of this paper that a rope should not 
bend over a wheel less than .,000 ties the diameter of the largest 
individual wire in the roi>e. This 'niili up on a.suming .S ._ 30.000 
from which we have U = .10,000,0c . d = 1,000 d. This only implies, 

.30,000 
afur all, that if 1) is greater than 1.000 d the life of the rope will be 
greater and ria- :rrsa. 

A prominent rope-maker in Kngland answers a letter of enquiry 
from us asking his rule by which to calculate the siie of wheel for a 
given size of rope as follows :— 

'• In haulage it is advisable to u.se the larg :si pulleys vou can 
possibly get in; this however is governed a great deal'by 'the con- 
ditions under 4vhich you have 10 work, and when we know the sue of 
the pulleys you are using we can generally suggest to you the class of 
rope most suitable. There is no rule for this, but it is purely a matter 
of experience and how ropes have worked under similar conditions in 
other places." 



The Canadim, Mimng InUituU. 



E= Modulus of e;ast/rit» ...i,; u ■ U 

can U 30.cco,ooo. pounC'r^^.e •„:! ^■■"""^- ^'^ ^'"' ^ -" 
d — Diameter of a sinele wirp nf .h- 
D_= Diameter of pu4;~:'''"''^ ■"■-''"■ 

-^i^e ofThe'lTer;::: '■"^'' '''"^"°" -- -<^ "P™ -^^ oute™„« 

-^e'rS:^:-::;^J-f-.;''e diameter Of .e outer 

-e on,, for conveni^ce^eCd -°:8""": ""■""" °' -■- ("ere 

S ^ JL = 30,000,000 .08 inch ~, "„'"' " = «° '-''"• 
j^ -uo men -_ 30,000 lbs. 

.„, 80 inches. 

ihe cross sectional area nf ih. . 

ample is:_ * °' ">' '"^ ^'^es of wire in that ex- 

•35388227 X 30,000 lbs = ,„fi ,; ,u -35388227 

The stress produced on ,J, ^^ '""' ''"^ '" lending, 
^idered in conne'ction ^W. h h ' ,"::'™ T 1 '"""'"'' ">-' "-- 
a-ve a. the total stress. iV:;;"''""^''^ ''>^ '-d in order .0 

-^a..at.hesum Of these t.o sir iirr:::::;!: 

'o.«5^r:;^rnV:^;:tr--we.lo.eda,oad 
"TiTtJT" 3 + safe factor. 



On Hire Ropes. 



bending " 
lut of the 

and the 
ch must 

= K d^ 

we will 



outer 
: (here 
hes. 



con- 
•r to 
it is 
the 

)ad 



In the example the factor 6 was allowed to overcome bending 
stress, sudden jerks, etc. By finding the bending stress we see that 
factor a of 3 is ample to pnt up for the other possible stresses. .^ 
threefold security is considered sufficient. 

Whatever may be the relation of these two stresses, pulling and 
bending, the total stress on the rope will be that due to the com 
bination of these two stresses. 

If D is made so small that the two stresses, pull and bending, are 
d 
greater than the clastic limit the rope will receive a permanent set 
which, however, is not always dangerous. 

In this connection we might call attention to the baneful effect 
attending the use of wire ropes where reverse bends are made. Care 
ful record and e.xperiment have shown that the life of the winding rope 
which goes over the pit-head pulley and under the drum is only from 
one-half to three-quarters as great as the rope which goes over the pit- 
head pulley on to the top of the drum. 

The importance of greasing ropes is also accentuated by Mr 
Biggarfs tests. Two lengths of the same size and manufacture of rope 
were used; the unoiled length made only 16,000 wherea.. the oiled 
length made 38,700 bends over the same pulley before breaking. 
Other similar pieces of rope unoiled would run over a 24 inch pulley 
74,000 times, and the oiled length 386,000 times. 

This paper has assumed proporiions we had not intended when 
undertaking its compilation, and indeed it has been compiled on lines 
that wc had not intended when commencing it. Such a paj.er as this 
cannot be considered complete without considering many other im- 
portant points in wire rope construction, and its use, such as the 
neutral axis, the proper diameter of sheaves, curves, etc. At some 
future time we may send in another paper covering these important 
points.